1. Field of the Invention
This invention relates to a method and apparatus for indicating the presence of an individual adjacent to a vehicle which is about to be placed in motion. The invention relates more particularly to a safety method and apparatus which will indicate to a vehicle operator the dangerous proximity of a person adjacent the vehicle.
2. Background of the Invention
The need often arises for indicating to the operator of a vehicle the presence of an individual in an area about the vehicle and which presence constitutes a hazard to the safety of the individual as the vehicle is placed in motion. Such vehicles are characterized by a limited, restricted visibility and include an area which cannot be adequately viewed by the vehicle operator from his station prior to initiating vehicle motion. While backing vehicles are generally recognized to have areas obscured to the operator directly rearward of the vehicle, limited areas forward of the vehicle can also be obscured to the operator.
Restricted visibility is particularly important with respect to school buses which transport young children who are exposed daily to a potential hazard resulting from obscured operator viewing. While various precautions have been taken in the operation of school buses, the physical size of grade school children, the restricted operator viewing and a propensity for young children to quickly dart into an obscured area of the bus unknowing to the operator have all contributed to fatalities in the operation of school buses. It is found that the forward portions of some school buses obstruct the operator's view of the ground area immediately in front of the vehicle for a distance of several feet. Children have been known to alight from a bus, traverse this area, and suddenly and unknown to the operator, dart back in front of the bus at times resulting in fatalities.
Various means have been provided in order to aid the operator in sensing the presence of individuals about the vehicles. One well known technique provides for an array of mirrors which are oriented for operator viewing of a normally obscured area. While reflector systems of this type have operated satisfactorily to a limited extent, a safety system relying solely on reflective mirrors suffers from the important defect that at times the operator will, for various reasons, fail to tuilize this viewing system, or at times, the operator's attention is momentarily diverted at a critical moment from this viewing task by surrounding circumstances. In the case of school buses, such distraction is frequently caused by the activity and movement of children about the interior of the bus. The importance of safety with respect to operation of school buses and the potential fatalities which can arise has resulted in augmenting the school bus operator's viewing system with a monitor adult rider whose sole purpose is to verify clearance of persons about the bus prior to initiating motion. This approach not only substantially increases the cost of operating a school bus, but the technique fails when the adult monitor rider, for various reasons, is unable to attend to this task. Additionally, in order to restrict passage of children through a blind area forward of the bus, several mechanical means comprising extensible, elongated rods have been provided which rotate outwardly from a retracted position of the bus. Upon extension, the rods restrict children from passing through the blind area in front of the bus. These rods, while effective to a large extent, can be and have been defeated by playful and persevering children.
Capacitive proximity detectors are known and have been utilized in various sensing applications. These detectors generally include a capacitance which is formed between a stationary electrode and earth ground and which capacitance is included as an arm of a balanced bridge circuit. The movement of an object into an electric field existing between the electrode and earth ground, or, the departure of an object from the area, alters the capacitance, unbalances the bridge and a resulting indication is provided. While capacitive proximity detectors are used as stationary detectors, their usefulness with vehicles which repeatedly travel from one location to another and which experience continuous road variations and varying environmental conditions have heretofore been impractical as a vehicle safety device for sensing the proximity of individuals adjacent the vehicle. Moreover, various factors including relatively rapid ingress and egress of parties to the area of the electric field, a variation in capacitance caused by different environmental factors surrounding a stationary vehicle such as rocking and deflecting of the vehicle by parties boarding and disembarking the vehicle, movement of objects within the field during a pause of the vehicle at a location and other conditions including rain, snow, ice and dirt accumulations on an external electrode, all contribute to rendering the capacitance type of bridge circuit susceptible to repeated false indications.
It would be beneficial to provide a capacitive proximity detector for use on a vehicle which is relatively stable in operation and which reduces susceptibility to false indications.